A hard disk drive for a magnetic disk, such as a hard disk, has a voice coil motor for driving an arm that supports a magnetic head. The voice coil motor is controlled to position the magnetic head onto a desired position over the magnetic disk, whereby recording/playback of information is performed thereon.
In recent years, there have been proposed magnetic disk drives of the type that, in addition to a coarse regulation actuator, such as a voice coil motor and the like, has a fine adjustment actuator, i.e., so-called two-stage or dual-stage actuator, formed from a piezoelectric element or the like and provided to the arm for further improving the positioning accuracy.
FIG. 8 shows the magnetic disk drive as conventional examples of a feedback control system including a dual-stage actuator. FIG. 8(A) shows a conventional example in which a coarse adjustment control system VS, which is inclusive of a coarse adjustment control actuator V and a coarse adjustment control circuit Cv therefore, and a fine adjustment control system PS, which is inclusive of a fine adjustment actuator P and a fine adjustment control circuit Cp therefore, are provided independently of one another.
In this case, the coarse adjustment control circuit CV controls the coarse adjustment actuator V so that the magnetic head is moved towards the desired position. In an alternative expression, the coarse adjustment control system VS is designed to be a stable system in which a current position of the magnetic head is converged to a desired position corresponding to a stable point. The fine adjustment control system PS also is similarly designed.
Nevertheless, however, the thus designed coarse adjustment control system VS is slow in response speed in comparison to the fine adjustment control system PS, such that the operation of the course adjustment actuator V serves as hindrance to the extent of increasing a time period necessary for positioning the magnetic head.
A technique can be contemplated that causes the coarse adjustment actuator V to substantially not operate, but causes the positioning of the magnetic head to be achieved only with operation of the fine adjustment actuator P. However, only with the operation of the fine adjustment actuator P, the time period necessary for positioning the magnetic head cannot be reduced.
FIG. 8(B) shows a conventional example in which the coarse adjustment control circuit Cv utilizes a control value output form the fine adjustment control circuit Cp. In this case, since the coarse adjustment control circuit Cv calculates the control value after the fine adjustment control circuit Cp has calculated the control value, a time period is taken until the coarse adjustment control circuit Cv outputs the control value to the coarse adjustment actuator V.